Buggy code:
public class WebPage < T > extends Page < T > implements INewBrowserWindowListener { private static final class PageMapChecker < T > extends AbstractBehavior implements IHeaderContributor { private static final long serialVersionUID = 1L ; private final WebPage < T > webPage ; PageMapChecker ( WebPage < T > webPage ) { } @ Override public final void renderHead ( final IHeaderResponse headResponse ) { } } private static final Logger log = LoggerFactory . getLogger ( WebPage . class ) ; private static ResourceReference cookiesResource = new ResourceReference ( WebPage . class , "cookies.js" ) ; private static final long serialVersionUID = 1L ; private UrlCompressor compressor ; protected WebPage ( ) { } protected WebPage ( final IModel < T > model ) { } protected WebPage ( final IPageMap pageMap ) { } protected WebPage ( final IPageMap pageMap , final IModel < T > model ) { } protected WebPage ( final PageParameters parameters ) { } protected WebPage ( final IPageMap pageMap , final PageParameters parameters ) { } @ Override public String getMarkupType ( ) { } public final UrlCompressor getUrlCompressor ( ) { } public void onNewBrowserWindow ( ) { } private void commonInit ( ) { } @ Override protected void configureResponse ( ) { } protected void setHeaders ( WebResponse response ) { } protected final WebRequestCycle getWebRequestCycle ( ) { } protected final BookmarkablePageLink homePageLink ( final String id ) { } @ Override protected void onAfterRender ( ) { super . onAfterRender ( ) ; if ( DEVELOPMENT . equals ( WebPage . getApplication ( ) . getConfigurationType ( ) ) ) { HtmlHeaderContainer header = ( ( HtmlHeaderContainer ) ( WebPage . visitChildren ( new IVisitor < org . apache . wicket . Component < ? > > ( ) { public Object component ( org . apache . wicket . Component < ? > component ) { if ( component instanceof HtmlHeaderContainer ) { return component ; } <START_BUG> return IVisitor . CONTINUE_TRAVERSAL_BUT_DONT_GO_DEEPER ; <END_BUG> } } ) ) ) ; if ( header == null ) { header = new HtmlHeaderContainer ( HtmlHeaderSectionHandler . HEADER_ID ) ; add ( header ) ; Response orgResponse = WebPage . getRequestCycle ( ) . getResponse ( ) ; try { final StringResponse response = new StringResponse ( ) ; WebPage . getRequestCycle ( ) . setResponse ( response ) ; renderHead ( header ) ; final HtmlHeaderContainer finalHeader = header ; WebPage . visitChildren ( new IVisitor < org . apache . wicket . Component < ? > > ( ) { public Object component ( org . apache . wicket . Component < ? > component ) { component . renderHead ( finalHeader ) ; return CONTINUE_TRAVERSAL ; } } ) ; response . close ( ) ; if ( ( response . getBuffer ( ) . length ( ) ) > 0 ) { WebPage . log . error ( "^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^" ) ; WebPage . log . error ( ( ( "You<seq2seq4repair_space>probably<seq2seq4repair_space>forgot<seq2seq4repair_space>to<seq2seq4repair_space>add<seq2seq4repair_space>a<seq2seq4repair_space><body><seq2seq4repair_space>or<seq2seq4repair_space><header><seq2seq4repair_space>tag<seq2seq4repair_space>to<seq2seq4repair_space>your<seq2seq4repair_space>markup<seq2seq4repair_space>since<seq2seq4repair_space>no<seq2seq4repair_space>Header<seq2seq4repair_space>Container<seq2seq4repair_space>was<seq2seq4repair_space>\n" + "found<seq2seq4repair_space>but<seq2seq4repair_space>components<seq2seq4repair_space>where<seq2seq4repair_space>found<seq2seq4repair_space>which<seq2seq4repair_space>want<seq2seq4repair_space>to<seq2seq4repair_space>write<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space><head><seq2seq4repair_space>section.\n" ) + ( response . getBuffer ( ) ) ) ) ; WebPage . log . error ( "^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^" ) ; } } catch ( Exception e ) { WebPage . log . error ( "header//body<seq2seq4repair_space>check<seq2seq4repair_space>throws<seq2seq4repair_space>exception" , e ) ; } finally { this . remove ( header ) ; WebPage . getRequestCycle ( ) . setResponse ( orgResponse ) ; } } } } }

Fix:
return IVisitor . CONTINUE_TRAVERSAL ;